Time is requested on beam line 9-1 or 7-1 at SSRL for high resolution structure determination of three different protein systems. One system involves viral proteins that inhibit apoptosis, an active process by which organisms remove superfluous cells. Apoptosis is vital to normal organismal development and tissue homeostasis. Currently one protein, p35, has been cloned, crystallized, and its structure has been determined using x-ray energy from a rotating anode. Additionally, my laboratory is actively pursuing crystallization of complexes between the viral protein and the cellular enzyme in which it binds and inhibits. The second system involves proteins that assimilate inorganic sulfur from the environment into living organisms. Currently crystals have been obtained of APS kinase, which catalyzes the second step in sulfur activation. We are also vigorously pursuing crystallization of the enzyme, ATP sulfurylase, which cayalyzes the first committed step. The last system for which time is requested in on a ubiquitin-like protein (RUB1) that is implicated in cell cycle regulation. This small protein structure was determined using crystals only 105m thick with in-house x-rays, which diffract to 1.7 E resolution. The high flux from SSRL will surely result in higher quality data at much higher resolution for all three protein structures.